The present invention relates to limiting voltage excursions in electrical circuits including suppressing transient voltage peaks, and, more particularly, to suppressing them quickly.
A “snubber” arrangement is used in electrical circuits where there is the possibility of large voltage peaks, or voltage “spikes”, occurring in those circuits, often immediately following a switch being opened in the circuit because of inductance in that circuit causing a transient voltage peak, i.e. an inductive “kick”. Such voltage spikes are deleterious to the switch because the large voltage causes an electrical discharge across the gap between the separating switch contacts as the switch is being opened leading to damaging those contacts and so limiting the time to failure of that switch.
As an example, FIG. 1A shows a schematic diagram of a representative circuit, 1, in which power flows occur subject to being switched on and off. Circuit 1 contains an inductor, 2, taken to have an inductance of 100 μH representing circuit parasitic inductance, and a resistor, 3, taken to have a value of 0.03 Ω representing a circuit electrical load in this large electrical power circuit. Further, there is provided a power flow control switch, 4, having an electrical resistance when the contacts thereof are closed of 0.2 Ω. All of the foregoing components are connected in series with one another and across a direct current voltage source, 5, providing 25 V of electrical potential between its two terminals.
An available simulation of the performance of this circuit upon an opening of switch 4 following a closing thereof at least long enough for the associated transients to subside does not simulate an actual electrical discharge occurring across the gap developing between the separating ideal switch contacts in opening of the switch to show the full effect of the circuit parasitics. However, the graph in FIG. 1B has an upper plot of the simulated voltage response with the simulation data points marked with squares to the opening of switch 4, and a lower plot of the corresponding current response with simulation data points being marked with triangles, both absent any effects due to the accompanying the discharge across the contacts separation gap. The upper plot shows, nevertheless, a voltage response greater than 35 kV at its peak. This is a peak value that is large enough to cause an arc discharge across the gap developed between the opening switch contacts such as occurs in the opening of the contacts of a typical relay. Though the lower plot shows the circuit current decreases to zero following this switching event, there is still substantial current in the circuit at the time of occurrence of the voltage spike to thereby result in a corresponding electrical power spike. Without a snubber arrangement of some kind across switch 4, this transient voltage peak and the associated arc discharge will damage, and so reduce the operational duration of, the switch contacts.
In the past, a complex of inductors and capacitors were often used in a filter configuration in providing such snubber arrangements. These configurations tended to be relatively large. Alternate arrangements used in these applications are Zener diodes and transient voltage suppressors, or transorbs, and Zener diodes have also been used as circuit “clamps” to similarly limit circuit operating voltage excursions to some maximum or minimum value. While these devices are much smaller than the filter arrangement, the response and power rating of these devices make their suitability in substantial power handling circuits limited. Thus, there is a desire for a snubber arrangement suited to circuits carrying large power flows but which provide snubbers of relatively small size and rapid reaction.